MATLAB: Randomly select an element from a vector satisfying a condition

randomselection

Dear experts,

I would like to randomly select an element from a vector satisfying a condition. In fact, I want to know what is the fastest way. For example, suppose vector X defined as follows:

X = [1 2 3 4 5 2 3 6 7 8 8 7 9 10 0 1 2 3 8 5 6 4];

How should I randomly select and identify the index of an element in this vector, which is greater than 2?

Thanks for your help,

Amir

Best Answer

I already have an answer to this question as follow (but I am seeking for faster solutions):

Ind = find(X > 2); Ind = Ind(randsample(1:numel(Ind), 1));

Related Solutions

MATLAB: Array indexing question for vectorization

You can try the following trick

c = unique(IND)
d = accumarray(IND',B',[],@prod)
A(c) = A(c).*d(c)'

MATLAB: Choose one out of every 8 elements randomly

m = 21;
A = (1:m)+0.314;
nof8 = ceil(m/8);
randSelect = randi([1 8],1,nof8);
inds = randSelect+(0:nof8-1)*8;
% if m is not a multiple of 8 the last samples must get special treatment
% the simplest solution is to limit the indices in inds to the m
inds(end)=min(inds(end),m);
% but this leads to a non-uniform distribution for the last selection.
selectedElements = A(inds)

A solution with an uniform distribution for all cases was suggested from Guillaume:

 randselect = randi(8, 1, floor(numel(A)/8));
 if mod(numel(A), 8) > 0 
   randselect = [randselect, randi(mod(numel(A), 8))];
 end
 selectedvalues = A(randselect + (0:ceil(numel(A)/8)-1)*8)

Best Answer

Related Solutions

MATLAB: Array indexing question for vectorization

MATLAB: Choose one out of every 8 elements randomly

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